In general, known systems for storage of radioactive waste have been undesirable with regard to safety and engineering assurance, simplicity, cost and efficiency, political and social support, and combinations thereof. Prior systems have been expensive, time-consuming to use, and face serious political and social challenges. Mined geological repositories have especially shown inflexibility and other challenges.
Nevertheless, numerous factors suggest that deep borehole storage of radioactive waste is inherently safe. Several lines of evidence indicate that groundwater at depths of several kilometers in continental crystalline basement rocks has long residence times and low velocity. High salinity fluids have limited potential for vertical flow because of density stratification, which also prevents colloidal transport of radionuclides. Geochemically reducing conditions in the deep subsurface limit the solubility and enhance the retardation of key radionuclides. A non-technical advantage that the deep borehole concept may offer over a mined geologic repository concept is that of facilitating incremental construction and loading at multiple, perhaps regional, locations.
Such storage would involve positioning of waste canisters at extreme depths of greater than 2,000 m and even to a depth of 5,000 m. Although different materials can be placed in a stratified configuration at such depths, prior configurations did not permit such materials to be secured to the walls of the borehole and, thus, may not adequately secure the waste canisters within the borehole.
Liquids present in such boreholes, such as, drilling fluid and/or naturally contaminated water well below the water table, can create additional challenges. For example, known bridge plugs for downhole drilling are sealed to prevent fluid transport from below the bridge plug to above the bridge plug. Such sealing renders known bridge plugs incapable of being used in conditions where fluid is to travel from below the bridge plugs to above the bridge plugs.
Known camming systems provide the ability to support certain objects. However, known camming systems are capable of being actuated from relatively short distances (such as, within 1 m and/or less than 50 m), involve weight-bearing portions being positioned below the camming system (thus, prohibiting their use to support objects above the camming system), are not available for high-pressure and/or submerged conditions, are not available for supporting heavy weights (such as, greater than 150 kg), or combinations thereof.
A support system, an excavation arrangement, and a process of supporting an object that do not suffer from one or more of the above drawbacks would be desirable in the art.